Revise "Setup Application in Authgear" section on SDK Get Started pages about docs

[stanleylhs]

@joyzoursky Re: problem 3, the word URI is missing, it means Custom URI Scheme.

ref: https://developer.apple.com/documentation/xcode/defining-a-custom-url-scheme-for-your-app

[joyzoursky]

@stanleylhs Thanks, and we should have links for the internal / external references here, seem on some sdk get started pages there are part of the instructions for registering URL scheme. https://docs.authgear.com/get-started/ios#register-url-scheme-for-redirect-uri

[stanleylhs]

This is my end of day current draft. Will work on it later. Not sure how to clarify the JWT part yet.

1. From the Project listing, select an existing Project or Create a new Project with the button at the bottom.
2. Go to "Applications" on the left menu bar.
3. Click "⊕Add Application" in the top tool bar.
4. Input the name of your application, e.g. "AwesomeApps", make a note of this for future references.
5. Under "Authorized Redirect URIs", Click "⊕Add URI"
6. In your target platform IDE (e.g. XCode / Android Studio), define a custom URI scheme that the users will be redirected back to your app after they have authenticated with Authgear. See external info below.
7. Head back to Authgear Portal, paste in the URI that you have defined in the previous steps, e.g. com.myapp.example://host/path
8. Click "Save" in the top tool bar.
9. Make a note of the generated "Client ID". You can also obtain the "Client ID" from the list again.

If you wish to validate JSON Web Token (JWT) in your own application server, select "Issue JWT as access token". If you wish to forward authentication requests to Authgear Resolver Endpoint, leave this unchecked. See comparisons in Backend Integration.

Ref for Custom URL scheme:
iOS https://developer.apple.com/documentation/xcode/defining-a-custom-url-scheme-for-your-app
Android https://developer.android.com/training/app-links/deep-linking